Rotary electric machine for a permanent magnet synchronous motor

ABSTRACT

A rotary electric machine comprises a rotating shaft  7  rotatably supported by bearings  2, 3 , a rotor  23  attached integrally with the rotating shaft  7 , and a stator  5  arranged facing the rotor  23 . The stator  5  includes a plurality of coils arranged substantially in a circular (annular) form in a rotating direction of the rotating shaft  7 . The rotor  23  includes a circular-disc rotor yoke  26  made of a ferromagnetic material, such as iron. Depressed portions and raised portions  28  on a surface of the rotor yoke  26  facing the stator  5 , except for the center portion, are arranged in a circumferential direction of the rotor yoke  26 . N-pole magnets  29  and S-pole magnets  30  are alternately arranged in the depressed portions  27 . Therefore, in addition to torque generated by the magnets  29, 30 , reluctance torque is generated between the raised portions  28  on the rotor yoke side  26  and the teeth on the stator side  25 , thus making it possible to increase the range of rotation speeds of the motor.

TECHNICAL FIELD

The present invention relates to a rotary electric machine applied to PMmotors (permanent magnet type synchronous motors) used in electricmotorcars.

BACKGROUND ART

Among axial-gap type PM motors, one that is shown in FIG. 13 has beenwell known.

As shown in FIG. 13, this motor is so structured as to be arranged in ahousing (frame) 1, and comprises a rotating shaft 7 rotatably supportedby bearings 2, 3 fixed to the housing 1, a rotor 4 integrally attachedto the rotating shaft 7, and a stator 5 arranged facing the rotor 4 andfixed to the housing 1.

The rotor 4 is made of a circular disc 6 of a ferromagnetic material,such as iron, and the rotating shaft 7 is mounted at the center of thedisc 6 and rotatably supported at both ends thereof by the bearings 2,3. On the surface of the circular disc 6 which faces the stator 5,N-pole magnets 8 and S-pole magnets 9 are arranged alternately in thecircumferential direction as shown in FIG. 14.

The stator 5 comprises an annular stator yoke 10 fixed to the housing 1,and a plurality of teeth 11, which are press-fitted in a plurality ofholes formed in the circumferential direction of the stator yoke 10. Thestator teeth 11 are wound with coils 12 of wire.

Meanwhile, in electric cars, an in-wheel motor is mounted in the wheelto realize independent drive of the wheel. The in-wheel motor, whichincludes a reduction gear (change gearbox), is required to be flatterand thinner in structure. Flat-type PM motors such as the one mentionedabove will find application as an in-wheel motor with a reduction gear.

In conventional axial-gap PM motors mentioned above, however, becausethey are incapable of utilizing reluctance torque, when they are usedfor in-wheel motors in electric-powered cars, there is a problem thatthe available range of rotation speed N is narrow.

Incidentally, the above-mentioned axial-gap type PM motor may be used asa generator.

Therefore, when used in a motorcycle or the like, in addition to the useas a starter motor to start the engine, and after the engine hasstarted, this motor may be switched to a generator mode by using thedriving force of the engine. This motor is hereafter referred to astarter-motor-cum-generator.

In other words, the starter-motor-cum-generator is used as a startermotor to start the engine and after the engine has started, it is usedas a generator.

When the axial-gap type motor is used as a starter-motor-cum-generatoras described above, the motor needs to generate a high torque to startthe engine. A general method to realize a high torque has been toincrease the magnetic force of the magnet of the motor.

With a conventional axial-gap type motor, since there is little hopethat this motor gives reluctance torque, there has been no other choicebut to increase the magnetic force of the magnet.

However, when the axial-gap motor is used as the starter-cum-generator,after the engine has started, the motor switches its operation to agenerator mode, and need not generate a high torque. On the contrary, ifthe magnetic force of the motor magnet is increased to generate a hightorque, when the generator is driven at high speed to generate electricpower, the battery is likely to be overcharged, so that it is necessaryto provide a voltage reducing circuit to protect batteries.

If the starter-motor-cum-generator is to be formed by using an axial-gapmotor, the magnetic force of the motor magnet is desired to be large tosecure a high torque at low rotation speed (when starting a car).However, to suppress overcharging of the battery at high rotation speed,there arises a contradictory demand to reduce the magnetic force of themotor magnet.

Therefore, an object of the present invention is to provide a rotaryelectric machine which is capable of utilizing reluctance torque whenthis rotary electric machine is used as a motor and thereby increasingthe range of rotation speeds of the motor.

Another object of the present invention is to provide a rotary electricmachine capable of preventing overcharge of the battery in itshigh-speed rotation and obviating the use of the voltage-reducingcircuit when the rotary electric machine is used astarter-motor-cum-generator in vehicles, such as motorcycles.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a rotary electricmachine comprising a stator having a plurality of coils arranged in asubstantially circular form around an axis and a rotor rotatable aboutthe axis relative to the stator, wherein the rotor comprises a rotoryoke facing the coils and having a gap in axial direction, wherein therotor yoke is made of a circular disc of a ferromagnetic material, andwherein depressed and raised portions are provided alternately in acircumferential direction on a surface of the rotor yoke facing thecoils, and N-pole magnets and S-pole magnets are alternately arranged inthe depressed portions.

According to the present invention of a structure described above, theraised portions are formed between the N-pole magnets and the S-polemagnets on the rotor yoke side, and the raised portions face the coilson the stator side. Therefore, supposing that the invention is a motor,a reluctance torque can be generated between the raised portions on therotor yoke side and the teeth (coils) of the stator side, making itpossible to increase the range of rotation speed of the motor.

According to the present invention, since raised portions are providedon the rotor yoke, the quantity of the magnet in use can be reduced byan amount due to that structural betterment than before, which makes itpossible to decrease production cost.

Further according to the present invention, the magnetic force of themagnet can be made smaller than before, but a reluctance torque can begenerated as described above. Therefore, when this invention is appliedin forming a starter-motor-cum-generator for vehicles, such asmotorcycles, a high torque can be obtained by using the reluctancetorque at low rotation speed (as in starting a car), and because themagnetic force of the magnets is made small, the battery is preventedfrom being overcharged at high rotating speed, a fact which obviates theneed to use the voltage-reducing circuit.

Further according to the present invention, there is provided a rotaryelectric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein said rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, wherein the rotor yoke is made of a circular disc of aferromagnetic material, wherein a corrugated region having raised anddepressed cross-sections alternating with each other is formed in acircumferential direction of the rotor yoke and magnets are arranged inthe depressed portions, and wherein out of all depressed portions, inthose depressed portions on a surface side of the rotor yoke facing thecoils, N-pole magnets and S-pole magnets are arranged alternately.

According to the invention of the structure as described, on the rotoryoke side, the raised portions are formed, each sandwiched between anN-pole magnet and an S-pole magnet, and the raised portions face thecoils on the stator side. For this reason, when the present invention isapplied in forming a motor, it is possible to generate a reluctancetorque at the raised portions on the yoke side in collaboration with theteeth on the stator side, and thereby increase the range of rotationspeed of the motor.

Further according to the present invention, the magnetic force of themagnet can be made smaller than before, but a reluctance torque can begenerated as described above. Therefore, when this invention is appliedin forming a starter-motor-cum-generator for vehicles, such asmotorcycles, a high torque can be obtained by using the reluctancetorque at low rotation speed (as in starting a car), and because themagnetic force of the magnets is made small, the battery is preventedfrom being overcharged at high rotating speed, a fact which obviates theneed to use the voltage-reducing circuit.

As an embodiment of the present invention, a ferromagnetic material isfurther applied to that surface side of the rotor yoke which does notface the coils.

According to the embodiment structured as described, the rotor yoke isimproved in mechanical strength and also the flux leakage from themagnet can be prevented.

According to the present invention, there is provided a rotary electricmachine comprising a stator having a plurality of coils arranged in asubstantially circular form around an axis and a rotor rotatable aboutthe axis relative to the stator, wherein the rotor comprises a rotoryoke facing the coils and having a gap in axial direction, and whereinthe rotor yoke is made of a circular disc of a ferromagnetic material,wherein N-pole magnets and S-pole magnets are mounted alternately in thecircumferential direction on a surface of the rotor yoke facing thecoils, and wherein salient portions facing the teeth of the coils areprovided at predetermined intervals in predetermined positions in thecircumferential direction of an outer periphery of the rotor yoke.

In this invention, as described, salient portions are provided along theouter periphery of the rotor yoke. As a result, a reluctance torque canbe generated in collaboration with the teeth of the stator side, so thatit is possible to widen the range of rotation speed of the motor.

Further according to this invention, the magnetic force of the magnetcan be made weaker than before, but a reluctance torque can be generatedas described above. Therefore, when this invention is applied in forminga starter-motor-cum-generator for vehicles, such as motorcycles, a hightorque is obtained by using a reluctance torque at low rotating speed(when starting a car), and when this electric machine is rotated at highspeed, because the magnetic force of the magnet is made small, thebattery is prevented from being overcharged and a voltage-reducingcircuit is not required.

As an embodiment of the present invention, the above-mentioned salientportions are formed as bent portions bent toward the stator side.

According to this embodiment, the bent portions are provided along theouter periphery of the rotor yoke. Therefore, if a motor is formedaccording to this embodiment, a reluctance torque can be generated atthe bent portions on the rotor yoke side in collaboration with the teethon the stator side, and therefore it is possible to increase the rangeof rotation speed.

Further according to the present invention, there is provided a rotaryelectric machine comprising a stator having a plurality of coilsarranged in a substantially circular form around an axis and a rotorrotatable about the axis relative to the stator, wherein the rotorcomprises a rotor yoke facing the coils and having a gap in axialdirection, wherein the rotor yoke is made of a circular disc of aferromagnetic material, and wherein a hollow part, in which a rotatingshaft is press-fitted, is formed in the center of the rotor yoke in amanner integrally with the rotor yoke and a circularly curved surface isformed at an extreme end of the hollow part.

According to the present invention structured as described, thecircularly curved surface at the extreme end of hollow part may be usedas a bearing to bear a thrust, and the rotor and the thrust bearing maybe combined into a single structure, by which the rigidity of thestructure for rotating the rotor can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the whole structure of an axial-gapmotor according to a first embodiment of a rotary electric machine ofthe present invention;

FIG. 2 is a plan view of the rotor in FIG. 1 as viewed from the statorside;

FIG. 3 is a fragmentary sectional view, taken in circumferentialdirection, of an essential part of the rotor in FIG. 2;

FIG. 4 is a plan view showing the structure of the rotor of an axial-gapmotor as viewed from the stator side according to a second embodiment ofa rotary electric machine of the present invention;

FIG. 5 is a fragmentary sectional view, taken in circumferentialdirection, of an essential part of the rotor in FIG. 4;

FIG. 6 is a sectional view of an essential part showing a modificationof the rotor shown in FIG. 4;

FIG. 7 is a sectional view showing the whole structure of an axial-gapmotor according to a third embodiment of a rotary electric machine ofthe present invention;

FIG. 8 is a plan view of the rotor in FIG. 7 as viewed from the statorside;

FIG. 9 is a sectional view showing the whole structure of an axial-gapmotor according to a fourth embodiment of a rotary electric machine ofthe present invention;

FIG. 10 is a plan view of the rotor in FIG. 9 as viewed from the statorside;

FIG. 11 is a sectional view showing the whole structure of an axial-gapmotor according to a fifth embodiment of a rotary electric machine ofthe present invention;

FIG. 12 is a plan view of the rotor in FIG. 11 as viewed from the statorside;

FIG. 13 is a sectional view showing an example of a conventionalaxial-gap motor; and

FIG. 14 is a plan view of the conventional rotor as viewed from thestator side.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe accompanying drawings.

Referring to FIGS. 1 to 3, the structure of a first embodiment will bedescribed in which the rotary electric machine of the present inventionis applied to an axial-gap motor. A motor according to the firstembodiment, which is disposed in a housing 1 as shown in FIG. 1,comprises a rotating shaft 7 rotatably supported by bearings 2, 3 fixedto the housing 1, a rotor 23 mounted integrally to the rotating shaft 7,and a stator 5 arranged facing the rotor 23 and fixed to the housing 1.

The stator 5 has a plurality of coils arranged in a substantiallycircular (annular) form about the rotating shaft 7. In other words, thestator 5 has an annular stator yoke 10 fixed to the housing 1. Aplurality of holes 10A are provided at predetermined intervals incircumferential direction of the stator yoke 10, and teeth 11 arepress-fitted into the holes 10A. The stator teeth 11 are each wound withcoils of wire 12.

The rotor 23 comprises a rotor yoke 26 made of a disc of ferromagneticmaterial, such as iron, and the rotating shaft 7 is mounted at thecenter of the rotor yoke 26 and is rotatably supported at each end bythe bearings 2 and 3. On that surface area of the rotor yoke 26 whichfaces the stator 5 exclusive of the center area (in other words, only onthat area of the surface squarely facing the stator 5), the depressedportions 27 and the raised portions 28 are attached by being alternatelyarranged in circumferential direction of the rotor yoke 26 as shown inFIG. 3. In the depressed portions 27, N-pole magnets 29 and S-polemagnets 30 are alternately placed and fixed as shown in FIGS. 2 and 3.

As described above, in the first embodiment, the N-pole magnets 29 andthe S-pole magnets 30 are arranged alternately on the rotor yoke 26, theraised portions 28 are formed between the magnets 29 and 30, and theraised portions 28 face the teeth 11 of the stator side 5. Therefore,according to the first embodiment, in addition to the torque generatedby the magnets 29 and 30, the reluctance torque is generated between theraised portions 28 on the rotor yoke side 26 and the teeth 11 (coils) onthe stator side 5, which makes it possible to increase the range ofrotation speed of the motor.

Further according to the first embodiment, in which the raised portions28 are provided on the rotor yoke 26, the used quantity of magnet can bemade smaller than before, and the production cost can be decreased.

Meanwhile, when applied to vehicles, such as motorcycles, the firstembodiment may be applied in forming a starter-motor-cum-generator. Morespecifically, the rotary electric machine can be used as a starter motorto start the engine, and after the engine has started, it can be used asa generator.

On the other hand, according to the first embodiment, the magnetic forceof the magnets 29, 30 can be made smaller than before, but a reluctancetorque can be generated.

Therefore, when the first embodiment is applied in forming astarter-motor-cum-generator for vehicles, such as motorcycles, a hightorque can be obtained by this electric machine by using a reluctancetorque when it is operated at low rotating speed (when starting a car),and when this electric machine rotates at high rotating speed, becausethe magnetic force of the magnets 29, 30 is decreased, the battery isprevented from being overcharged, and therefore a voltage-reducingcircuit is not required.

Referring to FIGS. 4 and 5, description will be made of the structure ofa second embodiment in which the rotary electric machine of the presentinvention is applied to an axial-gap motor.

A motor according to the second embodiment is structured such that therotor 23 of the motor of the first embodiment is used instead of therotor 33 shown in FIGS. 4 and 5; however, the other parts are the sameas in the motor according to the first embodiment and their structuraldescriptions are omitted.

As shown in FIG. 4, the rotor 33 comprises a disc rotor yoke 36 made offerromagnetic material, such as iron, and a rotating shaft 7 is mountedat the center of the rotor yoke 36.

The rotor yoke 36 has a corrugated region formed in circumferentialdirection of the rotor yoke except for the center region thereof, thecorrugated region has raised and depressed cross-sections alternatingwith each other in the circumferential direction of the rotor yoke(Refer to FIG. 5). Therefore, as shown in FIG. 5, in the circumferentialdirection of the rotor yoke 36, the depressed portions 37 and the raisedportions 38 are formed alternately on an upper surface side of the rotoryoke 36 and depressed portions 39 and raised portions 40 are formedalternately on a lower surface side of the rotor yoke facing the stator(not shown).

On both surfaces of the corrugated region, magnets 41, 42 are arrangedand fixed in the depressed portions 37, 39 as shown in FIG. 5. Further,the magnets 42 set in the depressed portions 39 on the lower surfaceside are magnetized such that N-pole magnets and S-pole magnets areformed (magnetized) alternately. The magnets 41, 42 should preferably beanisotropic-magnetized.

As described above, according to the second embodiment, on that surfaceof the rotor yoke 36 which faces the stator, raised portions 40 arearranged between the N-pole magnets and the S-pole magnets, and theraised portions 40 can face the matching teeth of the stator.

Therefore, according to the second embodiment, in addition to the torquegenerated by the magnets 42, a reluctance torque is generated betweenthe raised portions 40 on the rotor yoke 36 side and the teeth on thestator side, so that it is possible to increase the range of rotationspeed of the motor.

Moreover, according to the second embodiment, the rotor yoke 36 can beproduced at low cost by press working.

Further according to the second embodiment, the magnetic force of themagnets 41, 42 can be decreased, but a reluctance torque can begenerated as has been described.

Accordingly, when the second embodiment is applied in forming astarter-motor-cum-generator for a motorcycle or a similar vehicle, ahigh torque can be generated by using a reluctance torque at slowrotating speed (when starting a car), and when this rotary electricmachine is operated at high rotation speed, because the magnetic forceof the magnets 41, 42 is decreased, the battery can be prevented frombeing overcharged, and therefore a voltage-reducing circuit is notrequired.

A modified example of the rotor 33 will next be described with referenceto FIG. 6.

A rotor 45 in FIG. 6 is formed by integrally attaching a disc core 46 ofa ferromagnetic material to the upper surface of the rotor 33 shown inFIGS. 4 and 5. Consequently, the mechanical strength of the rotor 33 canbe increased and it is possible to prevent magnetic flux leakage fromthe magnets 41, 42.

Note that the other parts of the rotor 45 are identical in structurewith those of the rotor 33 and the same components are designated by thesame reference numerals, and their structural descriptions are omitted.

Referring to FIGS. 7 and 8, description will be made of the structure ofa third embodiment in which the rotary electric machine of the presentinvention is applied to an axial-gap motor.

A motor according to the third embodiment, which is disposed in thehousing 1 as shown in FIG. 7, comprises a rotating shaft 7 rotatablysupported by bearings 2, 3 fixed to the housing 1, a rotor 53 mountedintegrally to the rotating shaft 7, and a stator 5 arranged facing therotor 53 and fixed to the housing 1.

The rotor 53 comprises a rotor yoke 56 made of a disc of a ferromagneticmaterial, such as iron, and the rotating shaft 7 is mounted at thecenter of the rotor yoke 56 and rotatably supported at both ends thereofby the bearings 2, 3. On that surface which faces the stator 5 of therotor yoke 56 exclusive of the center area and the peripheral area (inother words, only on that area of the surface area squarely facing thestator 5), N-pole magnets 59 and S-pole magnets 60 are attached by beingalternately arranged in the circumferential direction as shown in FIG.8.

Radially-salient portions 58 are formed integrally with the rotor yoke56 at the positions on the outer circumference of the rotor yoke 56where the outer circumference is intersected by extensions of theboundaries between the N-pole magnets 59 and the S-pole magnets 60, asshown in FIGS. 7 and 8. Those salient portions 58 are provided togenerate reluctance torque in collaboration with the teeth of the stator5.

The stator 5 is basically the same in structure as the stator 5 shown inFIG. 1, but since the salient portions 58 are added to the rotor yoke56, the salient portions 11A to generate reluctance torque by coming toface the salient portions 58 are added to the teeth 11 of the stator.

As described above, according to the third embodiment, the salientportions 58 are added to the outer periphery of the rotor yoke 56, andthe salient portions 58 come round to face the salient portions 11A ofthe teeth 11 of the stator side 5. Therefore, according to the thirdembodiment, in addition to the torque generated by the magnets 59 and60, reluctance torque is generated between the salient portions 58 ofthe rotor yoke 56 and the salient portions 11A of the teeth on thestator side 5, and therefore it is possible to increase the range ofrotation speed of the motor.

Because the salient portions 58 are added to the outer circumference ofthe rotor yoke 56 in the third embodiment, their phase positionsrelative to those of the magnets 59, 60 can be optimized.

Further, according to the third embodiment, the magnetic force of themagnets 59, 60 can be decreased, but reluctance torque can be generatedas described above.

Therefore, when the third embodiment is applied in forming astarter-motor-cum-generator for vehicles, such as motorcycles, a hightorque can be obtained by using reluctance torque when thismotor/generator is rotated at low rotation speed (when starting a car),and when this motor/generator is rotated at high speed, because themagnetic force of the magnets 59, 60 is decreased, the battery can beprevented from being overcharged, and therefore a voltage-reducingcircuit is not required.

Referring to FIGS. 9 and 10, description will be made of a fourthembodiment in which the rotary electric machine of the present inventionis applied to an axial-gap motor.

The motor according to the fourth embodiment, which is disposed in thehousing 1 s shown in FIG. 9, comprises a rotating shaft 7 rotatablysupported by bearings 2, 3 fixed to the housing 1, a rotor 63 integrallyattached to the rotating shaft 7, and a stator 5 arranged facing therotor 63 and fixed to the housing 1.

The rotor 63 is made of a circular-disc rotor yoke 66 of a ferromagneticmaterial, such as iron, and the rotating shaft 7 is mounted at thecenter of the rotor yoke 66 and rotatably supported at both ends thereofby the bearings 2, 3. On that surface area of the rotor yoke 66 whichfaces the stator 5 exclusive of the center area and the peripheral area(in other words, only on that area of the surface squarely facing thestator 5), the N-pole magnets 69 and the S-pole magnets 70 are arrangedalternately in the circumferential direction of the rotor yoke 66 asshown in FIG. 10.

As shown in FIGS. 9 and 10, bent portions 68 bent down at right angle tothe stator side 5 are provided integrally with the rotor yoke 66 atpositions on the outer circumference of the rotor yoke 66 where theouter circumference is intersected by extensions of the boundariesbetween the N-pole magnets 69 and the magnets 70. Those bent portions 68are provided to generate reluctance torque in collaboration with theteeth of the stator 5.

The stator 5 is basically the same in structure as that of the stator 5shown in FIG. 1, but because the bent portions 68 are added to the rotoryoke 66, the teeth 11 are so formed as to generate reluctance torque asthey face the bent portions 68.

As described above, according to the fourth embodiment, the bentportions 68 are formed on the rotor yoke 66, those bent portions 68 comeround to face the teeth 11 of the stator side 5. As a result, accordingto the fourth embodiment, besides the torque generated by the magnets 69and 70, reluctance torque is generated between the bent portions 68 onthe rotor yoke 66, so that it is possible to enlarge the range ofrotation speed of the motor.

Further according to the fourth embodiment, since the bent portions 68are added to the outer circumference of the rotor yoke 66, their phasepositions relative to those of the magnets 69 and 70 can be optimized.

Further according to the fourth embodiment, because the bent portions 68are formed on the rotor yoke 66 in a manner to generate reluctancetorque, compared with third embodiment, the diameter of the rotor 63 canbe made smaller, and as a result, the diameter of the whole motor can bemade smaller.

Moreover, according to the fourth embodiment, the magnetic force of themagnets 69 and 70 can be decreased, but the reluctance torque can begenerated as described above.

Consequently, when the fourth embodiment is applied in forming astarter-motor-cum-generator for use in vehicles, such as motorcycles, ahigh torque can be obtained by using reluctance torque when thismotor/generator is running at low speed (as in starting a car), and whenthe motor/generator is running at high speed, because the magnetic forceof the magnets 69 and 70 is deceased, the battery can be prevented frombeing overcharged, making it unnecessary to use a voltage-reducingcircuit.

Referring to FIGS. 11 and 12, description will be made of a fifthembodiment in which the rotary electric machine of the present inventionis applied to an axial-gap motor.

The motor according to the fifth embodiment, which is disposed in thehousing 1 as shown in FIG. 11, comprises a rotor 73 rotatably supportedby bearings 2 and 3 fixed to the housing 1, and a stator 5 arrangedfacing the rotor 73 and fixed to the housing 1.

The rotor 73 includes a rotor yoke 76 and a rotating shaft 7 as shown inFIGS. 11 and 12. The rotor yoke 76 is formed of a disc entirely made ofa ferromagnetic material, and a hollow part 74, in which a rotatingshaft 7 is press-fitted, is formed in a manner integrally with the rotoryoke 76. A semispherical part (circularly curved surface) 75 is formedintegrally with the hollow part 74 at an extreme end thereof, and thesemispherical part 75 is used as a bearing to bear the thrust of therotor 73.

The hollow part 74 and the semispherical part 75 are formed by drawingwhen the rotor yoke 76 is formed in a monolithic body. In addition, thesemispherical part 75 is hardened to increase its mechanical strength.

The rotating shaft 7 is mounted integrally with the rotor yoke 76 at thecenter thereof by being press-fitted into the hollow part 74. Therotating shaft 7 and the hollow part 74 are supported at one end by thebearing 2 or 3, and the semispherical part 75 is arranged as a bearingto bear the thrust of the rotor yoke 76.

On that surface of the rotor yoke 76 which faces the stator 5 exclusiveof the center area, N-pole magnets and S-pole magnets 80 are attached bybeing arranged alternately in circumferential direction of the rotoryoke 76 as shown in FIGS. 11 and 12.

The stator 5 is the same in structure as the stator shown in FIG. 1, andthe same components are designated by the same reference numerals andtheir descriptions are omitted.

According to the fifth embodiment, the semispherical part 75 formedintegrally with an extreme end of the hollow part 74 can be used as abearing to bear the thrust, and further the thrust bearing can be formedintegrally with the rotor yoke 76. By this arrangement, the rigidity ofthe structure for rotation of the rotor 73 can be improved.

The rotor 73 of the fifth embodiment is designed based on theconventional rotor 4 shown in FIG. 13 and is structured by being addedwith the hollow part 74 and the semispherical part 75.

However, alternatively, it is possible to use the rotor based on therotor 23, 33, 45, 53 or 63 according to the first to fourth embodiments,and add the hollow part 74 and the semispherical part 75.

In the first to fifth embodiments, description has been made of caseswhere the rotary electric machine of the present invention is applied toan axial-gap motor and cases where a starter-motor-cum-generator forvehicles, such as motorcycles, is formed by this rotary electricmachine. However, the rotary electric machine according to the presentinvention can be applied as power generators of the types mentionedabove, in which case the structure of such a generator will besubstantially the same structure of the relevant embodiment.

INDUSTRIAL APPLICABILITY

According to the present invention, when the present invention isapplied as a motor, reluctance torque can be generated between theraised portions on the rotor yoke side and the teeth (coils) on thestator side, for example, by which it is possible to increase the rangeof rotation speed of the motor.

Further, according to the present invention, when the present inventionis applied in forming a starter-motor-cum-generator for vehicles, suchas motorcycles, a high torque can be obtained by using reluctance torquewhen this motor/generator operates at low rotation speed (as in startinga car), and when this motor/generator operates at high rotation speed,because the magnetic force of the magnets is made smaller, overchargingcan be prevented and a voltage-reducing circuit is not required.

1. A rotary electric machine comprising a stator having a plurality ofcoils arranged in a substantially circular form around an axis and arotor rotatable about said axis relative to said stator, wherein saidrotor comprises a rotor yoke facing said coils and having a gap in axialdirection, wherein said rotor yoke is made of a circular disc of aferromagnetic material, wherein N-pole magnets and S-pole magnets aremounted alternately in the circumferential direction on a surface ofsaid rotor yoke facing said coils, and wherein salient portions facingteeth of said coils are provided solely between N-pole magnets andS-pole magnets at predetermined intervals in the circumferentialdirection of an outer periphery of said rotor yoke.
 2. The rotaryelectric machine according to claim 1, wherein said salient portions arebent portions bent down to face said stator.